Method and composition for detecting odors in gaseous fuels



Oct. 28, 1969 v PEURIFQY ET AL 3,475,129

METHOD AND COMPOSITION FOR DETECTING ooons IN GASEOUS FUELS Filed Oct.19. 1966 mvznrrons:

3 PAUL v. PEURIFOY LITTLETON wooos THEIR AGENT United States Patent 3475,129 METHOD AND COMOSITION FOR DETECTING ODORS IN GASEOUS FUELS PaulV. Peurifoy, Pasadena, and Littleton A. Woods, Houston, Tex., assignorsto Shell Oil Company, New York, N.Y., a corporation of Delaware FiledOct. 19, 1966, Ser. No. 587,862 Int. Cl. GOln 31/06 US. Cl. 23-230 11Claims ABSTRACT OF THE DISCLOSURE A composition of matter and method ofdetecting odors in hydrocarbon fuels by addition to such fuels anodorous saturated heterocyclic organic sulfide which on contact with anabsorbent material impregnated with an acidic solution of an alkalimetal iodate, a carbohydrate adsorbent and an organic sulfoxide orsulfone, results in a color change.

This invention relates to an improved odorant detecting composition anddevice therefor. More particularly, the invention pertains to novelmeans for detecting odorized light hydrocarbon fuels such as naturalgas, liquefied petroleum gases commonly called LPG and various othertypes of gases and fuels used for homecooking or heating and forindustrial uses, odorized with a minor amount of 0.10 part or more permillion of a saturated organic heterocyclic sulfide compound containingat least 3 carbon atoms and sulfur as a heteroatom in the molecule.

Various odoriferous materials such as liquid mercaptan or aliphatic oraromatic sulfides or unsaturated cyclic sulfides, e.g., thiophenes, areused as odorants for gaseous fuels as warning means of leaks andpossible consequent existence of toxic and explosive hazards. Suchmaterials particularly the mercaptan, e.g., ethyl mercaptan, arenormally susceptible to oxidation resulting in products lacking indesired odor intensity and they are generally corrosive to variousmetals such as copper and iron with which such odorized gases are incontact. However, these materials particularly the mercaptans are usedas odorants for gaseous fuels such as liquid petroleum gas (LPG) andvarious reagents and tests have been devised for their detection asevidenced by reference to Anal. Chem., vol. 26, No. 3, March 1954, pages528-536, and to US. Patent 3,208,828.

A class of odoriferous materials useful for this purpose are saturatedheterocyclic organic sulfides which are more stable than the odorantsmentioned above and inhibit corrosion. These materials occur naturallyin petroleum oils and can be recovered from acid sludge formed duringthe acid treatment of light liquid hydrocarbons such as crackedgasoline, kerosene and the like by suitable means such as bydistillation. Thus, the acid sludge on distillation produces an oilycondensate which is rich in saturated heterocyclic sulfides known aspetroleum thiophanes, which materials possess excellent stability andare useful noncorrosive odorants for gaseous fuels. The acid sludge fromwhich the thiophanes are recovered can be first hydrolyzed to removeweak acids and the tars formed are subjected to distillation to recoverpetroleum thiophanes from the condensate. Pure thiophane ortetrahydrothiophene can also be used as an odorant.

While various tests, reagents and detector devices are known fordetecting odorous sulfur-containing compounds such as the mercaptans orcertain sulfides in light hydrocarbons as pointed out above, effectivemeans for detecting the presence of petroleum thiophane or purethiophane, e.g., tetrahydrothiophene, in gaseous fuels are unknown thusmaking it under various circumstances inadvisable to use, particularlywith personnel who are insensitive to the odor and for various otherreasons.

3,475,129 Patented Oct. 28, 1969 ice It has now been discovered that anexcellent reagent or composition for detecting small amounts of evenless than 10 ppm. of odorous saturated heterocyclic organic sulfidessuch as thiophanes in gaseous fuels such as natural gas, liquidpetroleum gas and the like can be readily accomplished by contactingsaid odorous fuel with a sorptive granular material, e.g., alumina orsilica gel impregnated with an acidic solution of an alkali metaliodate, a finely divided carbohydrate adsorbate and an organic sulfoxideand/or sulfone and noting change in color such as from white to yellowor if a dye is added to the silica impregnated composition such as ablue dye, the color change due to the presence of the saturatedheterocyclic organic sulfides would be from blue to green. The device orapparatus for detecting odorous compounds mentioned can be essentiallythe same as described in US. Patent 3,208,828 provided the detectingreagent or composition is the one described in the present invention.

Specifically, the chemical composition used to impregnate the sorptivegranular materials such as silica impregnating material include amixture in specific proportions so as to produce the desired colorchange of (1) an alkali metal iodate such as potassium iodate ormixtures of potassium iodate and palladium chloride; (2) a carbohydrateadsorbent such as starch or other suitable materials capable of forminga colored complex with iodine; and (3) an organic sulfoxide and/ororganic sulfones which functions as a sensitivity agent and due to itspresence increases the sensitivity of the chemical reagent compositionsseveral fold. Materials of this type include aliphatic, aromatic, cyclicand heterocyclic sulfoxides or sulfones and mixtures thereof, such asdimethyl, diethyl, dibutyl, dioctyl, methyl phenyl, ethyl phenyl,diphenyl, dicyclohexyl sulfoxides and/or sulfones of which preferred aredimethyl sulfoxide, diethyl sulfoxide, dimethyl sulfone and diethylsulfone and mixtures thereof.

The odor detecting apparatus or device can be essentially the same asdescribed in US. Patent 3,208,828 provided the detector tube fordetermining the odorants in gases or liquid fuel compositions containssilica gel or other suitable material impregnated with an acidicsolution of potassium iodate, starch and dimethyl sulfoxide. To conducta test using the device described in US. Patent 3,208,828, the fuel,e.g., LPG or natural gas, is allowed to vaporize and pass through thedetector into a rubber balloon which is used to measure the gas volume.When the balloon reaches a predetermined size, the sampling is stopped.The natural color change of the treated silica gel is white to yellow;however, if a small quantity of blue dye is added to the reagentsolution used to treat the silica gel, the color change is from blue togreen.

A typical preparation of a detecting reagent is as follows.

Potassium iodate solution:

1 part (by volume) 6 N H SO 3 parts (by volume) glacial acetic acid 1part (by volume) 0.3 M K10 Reagent solution (mix in order shown):

( 1) 0.005 g. PdCl (2) 0.67 ml. K10 solution (see above) (3) 0.33 ml.0.2% w. starch solution (containing 0.001% Hgl (4) 1.85 ml. distilledwater (5) 1.15 ml. dimethyl sulfoxide (Spectro grade) (6) 0.10 ml.methylene blue, 4.0 g./l.

This combined solution is added to 5.0 g. of 60-80 mesh Davison grade950 silica gel, stirred well and heated in a vacuum oven at 50 C. for 30minutes. The gel should be stirred at 10 minute intervals to preventformation of a crust. The dried gel is packed into 2 mm. ID glass tubesin 1 cm. sections separated by fine glass beads or sand. The packedtubes are sealed with a flame.

Essentially, the invention comprises the provision of a method and meansfor readily determining and measuring the saturated organic heterocyclicsulfides, e.g., petroleum thiophane or pure thiophane content of gaseousfuels, e.g., natural gas or LPG, by contacting the material with asupported chemical indicator as described above which changes color inthe presence of petroleum thiophane or pure thiophane and is so arrangedthat with the passage of a definitely readily ascertained volume of gas,the indicator will show the concentration of the thiophane in the fuel,e.g., LPG or natural gas or the like.

The following is a description of a specific embodiment of the inventionthrough which descriptive reference is made to the accompanying drawingshowing further details of the invention.

In the drawing,

FIGURE 1 is an elevation of the assembled apparatu connected to agaseous fuel, e.g., a LPG container, prior to test;

FIGURE 2 shows an elevation of the lower part of the apparatus after thetest;

FIGURE 3 is a plan of the standard volume ring shown in the FIGURES 1and 2; and,

FIGURE 4 is an enlarged sectional view taken along the lines 4-4 ofFIGURE 1.

Referring to FIGURE 1, a filled pressure cylinder of gaseous or liquidfuel, e.g., natural gas or LPG 1, having its regular shutoff valve 2 isinverted and connected by a high pressure flexible conduit 3 to anadapter or reducer 4 to one side of a needle valve 5. The other side ofthe needle valve 5 is connected by means of a T-piece 6 to tubular elbow7. A pressure gauge 8 is attached to the third arm of the T-piece 6. Theend of the elbow 7 is connected by a rubber connector 9 to a coiledmetal vaporizer tube 10. The other end of the vaporizer tube 10 isconnected by a rubber connector 11 to a detector tube 12. The detectortube is made of transparent material such as glass or plastic and isprovided with uniform sections of impregnated sorptive material, e.g.,silica gel 12a, having a white (or blue if dye is added) color andunimpregnated sections of purified sand 12!; having a white color. Thelower end of the detector tube is connected by a suitable rubberconnector 13 to the neck of a completely deflated rubber sac or balloon14.

The rubber balloon 14 is encompassed by a standard volume ring gauge 15which consists of an upper horizontal ring element 15a and twobase-forming straps 15b and 15c which are fitted together at rightangles by being suitably fastened as will be seen from FIGURE 3 of thedrawing.

The length of the treated sections of silica gel 12a is adjusted so thata color change of each section or zone corresponds to a level of 10 ppm.thiophane in a prescribed volume of vaporized fuel, e.g., LPG. The fuelwithout the odorant produces no color change. Above and below the silicagel strata is packed a plug of cotton 16 held in place by wedge 17.

Variations of the above procedure may be used. One of the acids or thestarch may be omitted in the procedure. However, the presence of acidand starch increases the distinctness of the color change upon exposureto the odorant. The palladium chloride may be omitted, but its presencehelps to retain the reacted colors for a longer period of time. Theconcentration of the reagent composition can be varied between widelimits in order to adjust the sensitivity; e.g., the amount of potassiumiodate stock solution applied may vary from 0.1 to 10 m1./5 g. silicagel. Since dimethyl sulfoxide affects the sensitivity, its volume may bevaried, e.g., between 0.1 and 2.0 ml., to achieve the desired response.Drying and activation of the treated silica gel may be carried out in anordinary oven or in a vacuum oven, and the activation time may vary from0.5 to 24 hours.

To load the detector tubes the following procedure can be used:

(1) Cut a 6-inch length of 4 mm. O.D. glass tubing and place a 0.10-0.15inch cotton plug about 1.5 inches from one end.

(2) Fill the tube with alternate layers of treated silica gel (0.047 g.)and purified sand (0.041 g.).

(3) Vibrate the tube after the filling process with a mechanicalvibrator. A completed tube consists of 3 or 4 layers of treated silicagel and 2 or 3 layers of purified sand.

(4) Place another cotton plug in the tube and pack down cotton from bothends.

(5) Seal both ends of the tube with a flame.

As will be appreciated, considerable variation is permissible in themanner of packing and in the physical dimensions of a completed odorantdetector tube.

Calibration of the detector tubes was established with LPG samplesprepared by adding a known weight of saturated heterocyclic organicsulfide, e.g., thiophane, to a known weight of liquefied propane.

The testing apparatus is operated as follows. With the valve 2 oncylinder 1 open, the needle valve 5 is gently and carefully opened to asmall extent so that a fuel, e.g., LPG, will pass through to metalvaporizer tube 10. Upon the release in pressure through the needlevalve, the fuel will expand and change to the gaseous state with thewithdrawal of heat from the metal walls on the conduits. The gas nextpasses through detector tube 12 containing the silica gel and sand units12a and 12b. Gas from the lower end of the detector tube 12 is conductedinto the empty balloon placed inside the gauge ring stand 15. The gasflow is continued at a slow rate until the balloon makes a snug fitinside the ring 15. The fuel flow is then turned off and the detectortube disconnected. The detector tube is observed to note the number ofbright yellow zones (or green) formed from the white (or blue)impregnated silica gel. If, for example, the device is used formeasuring the concentration of thiophane in the 0-30 parts per millionrange, three zones of impregnated silica gel in the detector areprovided. These zones are of such concentration of reagent that with thepassage of the volume of gas received in the balloon, thiophane in theconcentration of 10 p.p.m. by weight is reacted entirely in one zone.This reaction with the potassium iodate-sulfoxide mixture turns thecolor from white to a bright yellow (or blue to green). By counting thenumber of zones or fractions thereof colored yellow (or green), a rapiddetermination of the concentration of thiophane in the fuel can be made.When testing natural gas, the balloon is filled three times to take intoaccount the difference in molecular weight between methane and LPG.

Care must be taken to ensure that the needle valve is not opened rapidlyor opened to a fast rate of flow. With a rapid opening or fast rate offlow the rubber connections are liable to be blown off and the testnecessarily will have to be started over again. If too rapid a flow isused, the fuel, e.g., LPG, will not be completely vaporized in thevaporizer tube 10, consequently an inaccurate test can result.Observation will indicate whether or not liquid is entering the detectortube. If the ambient temperature is low the vaporizing of the fuel inthe metal vaporizer tube 10 can be aided by slightly warming the tube bycontact with the operators hand. In case of very low ambient temperaturethe vaporizer tube can be positioned so that it can be inserted into acontainer of hot water.

EXAMPLE A test was made on a propane cylinder to determine the thiophanecontent. A glass detector tube having sealed ends was, after the tipshad been broken off, inserted into the system. The detector tube hadthree equal length zones of impregnated silica gel separated by zones ofpurified sand. The needle valve 5 was opened slowly until 15 lbs.pressure reading was obtained on the pressure gauge 8. The LPG wasallowed to flow until the balloon was filled to a snug fit in the ringwhich had an internal diameter of 16.6 cm. A balloon when filling thestandard volume ring had a content of 2.4 liters of gas. The needlevalve was then turned off and the detector tube carefully removed fromthe system. It was noted that two impregnated zones of white color hadturned to a bright yellow and that approximately /5 of the third zonewas yellow. The complete yellow zones formed each corresponded to p.p.m.of thiophane in the volume of LPG passed, namely 2.4 liters. It wasestimated that the LPG contained approximately 22 ppm. of thiophane.This was confirmed by accurate laboratory analysis with a coulometrictitrator.

One of the advantages of our invention it should be noted, is that theyellow or green colored zones retain these colors for long periods oftime and the detector tubes can be filed for later reference.

The material we prefer for the granular sorptive carrier or support forthe indicator is silica gel, although other materials such as aluminacould be used. The size of the support granules is governed in part bythe crosssectional area of the detector tubes used. Instead of glasstubes, tubes of suitable clear plastic material could be employed, orglass tubes covered with a transparent plastic material could be used.Various other modifications may be made. For example, instead of rubberconnectors of the type shown in the drawing, pipe fittings of moldedplastic could be substituted, although this will require the further useof hand tools to effect an assembly of the apparatus, which wouldsomewhat detract from the simplicity of the method and apparatus setforth herein.

We claim as our invention:

1. A composition of matter for detecting odor in light hydrocarbon fuelcompositions containing a thiophane odorant consisting essentially of asorptive granular material selected from the group consisting of aluminaand silica gel impregnated with an acidic solution of alkali metaliodate in an amount of 0.1 to 5 ml. per 5 grams of the sorptivematerial, a carbohydrate adsorbant capable of forming a color complexwith iodine and an organic sulfur-oxygen-containing compound selectedfrom the group consisting of organic sulfoxide and organic sulfone andmixtures thereof in an amount sufficient to function on a sensitivityagent.

2. The composition of claim 1 wherein the iodate compound is potassiumiodate, the carbohydrate is starch, the organic sulfur-oxygen-containingcompound is dialkyl sulfoxide and the sorptive granular material issilica gel.

3. The composition of claim 2 wherein the dialkyl sulfoxide is dimethylsulfoxide.

4. The composition of claim 1 wherein the odorous saturated heterocyclicorganic sulfide is petroleum thiophane and is present in the fuel, thefuel is liquid petroleum gas and the solution impregnated in the silicagel is a mixture of potassium iodate, starch and dimethyl sulfoxide.

5. The composition of claim 4 wherein the fuel is natural gas.

6. The composition of claim 4 wherein the odorant is thiophane.

7. The composition of claim 6 liquid petroleum gas.

8. The method of detecting and determining the presence of a thiophaneodorant in a light hydrocarbon fuel under pressure which comprises thestep of:

(a) reducing the pressure on the fuel by metering restrictive means to apredetermined lower pressure;

(b) vaporizing the liquefied gas;

(c) flowing a predetermined volume of the vaporized liquefied gasthrough successive separate elongated beds of sorptive granular materialof a solution of an alkali metal iodate and mixtures thereof, the iodatebeing present in from 0.1 to 5 ml. per 5 grams of adsorptive material, acarbohydrate capable of forming a color complex with iodine and anorganic sulfur-oxygen-containing compound which upon contact withthiophane odorant changes color over a length which is dependent uponthe concentration of the thiophane in the fuel, a complete color changeof each of said alternate beds thereby indicating a predeterminedconcentration of thiophane; and, therefore,

(d) determining the number of separate elongated beds which have changedcolor as an indication of the total concentration of thiophane in thevaporized fuel.

9. The method of detecting and determining the concentration of odorantin liquefied petroleum gases under pressure as defined in claim 8 inwhich the alkali salt reagent is potassium iodate, the carbohydrate isstarch and the odorant is petroleum thiophane.

10. The method of detecting and determining the presence andconcentration of thiophane as in claim 9 in which the liquefiedpetroleum gas is propane.

11. The method of detecting and determining the presence andconcentration of thiophane as in claim 9 in which the fuel is naturalgas.

wherein the fuel is References Cited UNITED STATES PATENTS 2,094,270 9/1937 Hampton et al. 252408 XR 2,869,994 1/ 1959 Nevers et a1 48--197 XR3,208,828 9/1965 Peuritoy et al. 23232 XR 3,404,971 10/1968 Olund 48195OTHER REFERENCES Rapid Color Test for Mercaptan Odorant in LiquefiedPetroleum Gas, An Analytical Chemistry, no. 9, vol. 36, August 1964, pp.1853-1855.

MAYER WEINBLATT, Primary Examiner U.S. Cl. X.R.

